Arrangement for cooling of an electrical machine

ABSTRACT

In one aspect, an arrangement for cooling of an electrical machine is provided. The arrangement includes a rotor and a stator of the electrical machine, while an air-gap is between the rotor and the stator. The electrical machine includes an air-cooling-arrangement, which circulates air inside the electrical machine. The electrical machine includes a liquid-cooling-arrangement, which circulates cooling-liquid inside the electrical machine. The air-cooling arrangement and the liquid-cooling-arrangement are connected by an air-to-liquid heat-exchanger, which is applied to transport heat out from the electrical machine by the cooling-liquid.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of European Patent Office applicationNo. 08018800.6 EP filed Oct. 28, 2008, which is incorporated byreference herein in its entirety.

FIELD OF INVENTION

The invention relates to a cooling-arrangement of an electrical machine.

BACKGROUND OF INVENTION

In a preferred embodiment the invention relates to a huge electricalmachine, which is totally enclosed by a shell or housing.

Electrical machines needs cooling to dissipate heat, which is generatedduring its operation by an ohmic resistance, by iron hysteresis, etc.

It is possible to cool a small electrical machine by a heat-transferfrom the inside of the machine to its surface.

This is not possible for a large machine, which shows a relatively smallsurface per power rating and heat generation.

When a machine is installed indoor at a dry atmosphere it is possible tooperate the machine without a housing, so a cooling is achieved by thecirculation of ambient air through the machine.

But when the machine is installed under harsh conditions, like it is forgenerators being used in offshore wind-turbines, the electrical machineneed to be totally enclosed, so ambient air is not allowed to circulatethrough the machine. For this application dedicated cooling-systems arerequired.

SUMMARY OF INVENTION

One very common cooling-method is the circulation of air or anothergaseous medium inside the electrical machine, while the cooling-mediumis kept cool by a heat-exchanger. This cooling method disadvantageouslyrequires large gas-to-air or gas-to-water heat-exchangers. Furthermoreconsiderable additional power is required to circulate thecooling-medium inside the machine.

Another cooling-method of a generator, which shows a stator and a rotor,is the circulation of a liquid on a first side of the stator. This firstside to be cooled is opposite to an air gap, which is between the statorand the rotor. The stator shows a number of stacked laminate-plates,which carries metal-windings of stator-coils, so the heat is transferredfrom the metal-windings through the laminate-plates to thecooling-medium by conduction.

This cooling method suffers from a considerable temperature-gradient,which exists between the windings of the stator and thecooling-medium—due to a moderate heat-conductivity of thelaminate-plates. Because of this it is difficulty to maintain apredetermined winding-temperature, which is below a requiredmaximum-value.

Furthermore, this cooling-method is not as effective as the air-cooling,because winding-heads of the coils and the rotor itself is not cooled inthe same way.

Another cooling-method is to bring in liquid or gas for cooling-purposesinto slots of the laminate-plates, while these slots are used to carrythe metal-windings. To bring in the cooling-medium hollowceramic-cooling-pipes are used, which are expensive and difficulty tohandle.

The problem is that there is still no direct cooling-effect of thewinding-heads and of the rotor.

It is aim of the present invention, to provide an improved arrangementfor cooling of an electrical machine.

This aim is solved by the features of the independent claims. Preferredembodiments of the invention are described within the subsequent claims.

The inventive arrangement for cooling of an electrical machine comprisesa rotor and a stator of the electrical machine, while an air-gap isbetween the rotor and the stator. The electrical machine comprises anair-cooling-arrangement, which circulates air inside the electricalmachine.

The electrical machine comprises an liquid-cooling-arrangement, whichcirculates cooling-liquid inside the electrical machine. The air-coolingarrangement and the liquid-cooling-arrangement are connected by anair-to-liquid heat-exchanger, which is applied to transport heat outfrom the electrical machine by the cooling-liquid.

According to the invention the stator is cooled by help of aliquid-medium while additionally air is used for cooling ofwinding-heads of the stator and for the cooling of the rotor.

The cooling-arrangement according to the invention shows a number ofadvantages.

The stator is cooled efficiently with a liquid-cooling arrangement.

Winding heads of the stator and the rotor itself are cooled with anadditional separate circuit, so the lack of the missing direct coolingof the stator as described above is compensated.

The air cooling of the winding-heads of the stator and of the rotorrequires a smaller amount of air for cooling-purposes as the systemsdiscussed above according to the state of the art. So a large proportionof ventilation losses are reduced, typically by a factor of ⅓.

The cooling of the stator and of the winding head and/or the rotor istuned individually in a preferred embodiment, so unbalanced cooling isavoided.

As air is used directly for the cooling inside the electrical machine,large external air-ducts are avoided. It is therefore possible to keepthe electrical machine totally enclosed.

In a preferred embodiment the same coolant is circulated throughinternal radiators and the stator (either parallel or serial), so asimple arrangement is achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail by help of some figures,while:

FIG. 1 shows a generator as electrical machine, which is cooledaccording to the invention,

FIG. 2 shows a first detail of the generator referring to FIG. 1, and

FIG. 3 shows a second detail of the generator referring to FIG. 1 andFIG. 2.

DETAILED DESCRIPTION OF INVENTION

FIG. 1 shows a generator G in a cross-sectional view, while thegenerator G is cooled according to the invention.

The generator G consists of an outer rotor 1 and an inner stator 2. Theinner stator 2 is connected via bearings 3 with the rotor 1.

The rotor 1 wears a number of magnets 4, so the magnets 4 are locatedpartly into an air-gap AG. The air-gap AG is between the stator 2 andthe rotor 1.

The stator 1 consists of a number of stacked laminate-plates 5, whilethe laminate-plates 5 show a number of slots, which are shown in moredetail later. The slots of the laminate-plates 5 carry metal-windings ofstator-coils—shown in more detail later.

A part of the stator-coil exceeds the slots of the stackedlaminate-plates 5, forming winding-heads 6 of the stator-coil.

The laminate-plates 5 are fixed by two end-plates 15.

There is a fan 7 for air-cooling, while the fan 7 is connected with thestator 2. The fan 7 circulates air through the air-gap AG and throughthe winding-heads 6 inside the generator G, while the air-circulationoccurs as shown along a way w.

There is an air-to-liquid heat-exchanger 8, which is connected with thefan 7 for cooling-purposes.

The heat-exchanger 8 is connected with a cooling-liquid-inlet 9 and witha cooling-liquid-outlet 10, which are used to transport “colder”cooling-liquid to the heat-exchanger 8 and to remove “warmer”cooling-liquid from the heat-exchanger 8 to carry away heat from theair-to-liquid heat-exchanger 8 to an outer side of the generator G.

There are a number of hollow pipes 11, which are in a thermal contactwith the laminate-plates 5.

The hollow pipes 11 are made of metal in a preferred embodiment. A firstend of these pipes 11 are connected with the cooling-liquid-inlet 9,while a second end of the pipes 11 are connected with thecooling-liquid-outlet 10, so a cooling-circuit is built for the liquidcooling.

The fan 7 circulates cooling-air to cool down the rotor 1 and thewinding-heads 6 and to cool down the laminate-plates 5 in a (small)certain extent.

The heat from the air-cooling-system is then transferred to an ambientby help of the heat-exchanger 8, which is connected with thecooling-liquid-inlet 9 and with the cooling-liquid-outlet 10 for thatpurpose.

So a main part of a cooling-capacity by the cooling-liquid is used forthe cooling of the metal-windings, which are located into the slots.

There is a combination of air-cooling on one hand and of liquid-coolingon the other hand.

FIG. 2 shows a first detail along an intersection-line A-A of thegenerator G referring to FIG. 1.

There is a laminate-plate 5 of the stator 2, while the laminate-plate 5shows a number of slots 5 a.

Between the stator 2 and the rotor 1 is the air-gap AG, while the rotor1 shows a number of magnets 4, fixed at the rotor 1.

The hollow pipes 11 for the liquid-cooling are connected in thermalcontact with the laminate-plates 5 of the generator G.

FIG. 3 shows a second detail of the generator G referring to FIG. 1 andFIG. 2.

The slots 5 a of the laminate-plate 5 are used to carry metal-windings14 of a stator-coil (not shown in detail). While the first side of thelaminate-plate 5 is faced to the air-gap AG a second side of thelaminate plate 5 is in thermal connection with the laminate-plates 5 forcooling-purposes.

The second side is located opposite to the first side and is connectedvia welding 13 with the hollow pipes 11. So the welding 13 are used forthe thermal connection.

Inside this hollow pipe 11 the cooling-fluid is arranged to circulate toand from the heat-exchanger 8.

The hollow pipe 11 is in direct thermal contact with the laminate-plate5 of the stator 2 via the welding 13.

The described cooling-system with a welding-connection between thehollow-pipes 11 and the second side of the laminate plates 5, while thehollow-pipes 11 are located at the second side of the laminate-plates 5is a preferred embodiment of the invention.

In another preferred embodiment it is possible to enclose thehollow-pipes 11 by the laminate-plates 5, so the hollow-pipes 11 areforming an integrated part of the laminate-plates 5.

In another preferred embodiment it is possible to integrate thehollow-pipes 11 with the metal windings 14 or with the slots 5 a or tocombine the embodiments as described above.

In a preferred embodiment only “internal air” of the generator G iscirculated inside, so it is possible to encapsulate the generator Gcompletely. Only the liquid-cooling is used to remove the heat out fromthe generator G.

1.-15. (canceled)
 16. Arrangement for cooling of an electrical machine, wherein the electrical machine comprises a rotor and a stator, an air-gap is arranged between the rotor and the stator, the electrical machine comprises an air-cooling-arrangement that circulates air inside the electrical machine, the electrical machine comprises a liquid-cooling-arrangement that circulates cooling-liquid inside the electrical machine, and the air-cooling arrangement and the liquid-cooling-arrangement are connected by an air-to-liquid heat-exchanger, which is applied to transport heat out from the electrical machine by the cooling-liquid.
 17. The arrangement according to claim 16, wherein the stator comprises a plurality of laminate-plates, and the laminate-plates comprises a plurality of slots in which metal-windings of coils of the stator are arranged in the slots.
 18. The arrangement according to claim 16, wherein the stator is arranged as inner stator, while the rotor is arranged as outer rotor of the electrical machine.
 19. The arrangement according to claim 17, wherein the stator-coils exceed the slots of the laminate-plates to form winding-heads of the stator-coil.
 20. The arrangement according to claim 16, wherein the air-cooling arrangement comprises a fan.
 21. The arrangement according to claim 19, wherein the air-cooling arrangement is arranged to circulate air through the air-gap and through the winding-heads of the stator-coil.
 22. The arrangement according to claim 16, wherein the air-to-liquid heat-exchanger is connected with a cooling-liquid-inlet and with a cooling-liquid-outlet, which are used to transport cooling-liquid to and from the heat-exchanger to remove the heat.
 23. The arrangement according to claim 16, wherein the liquid-cooling-arrangement comprises hollow pipes to transport the cooling-liquid to and from the air-to-liquid heat-exchanger, and endings of the hollow pipes are connected with the cooling-liquid-inlet and with the cooling-liquid-outlet to form the liquid-cooling-arrangement.
 24. The arrangement according to claim 17, wherein a first side of the laminate-plates comprises the slots of the laminate-plate and where the first side of the laminate-plate faces toward the air-gap, and a second side of the laminate plate is opposite to the first side of the laminate plate and is in thermal connection with the liquid-cooling-arrangement.
 25. The arrangement according to claim 24, where the thermal connection is formed as a welding-connection.
 26. The arrangement according to claim 23, wherein the hollow-pipes are an integrated part of the laminate-plates.
 27. The arrangement according to claim 23, wherein the hollow-pipes form an integrated part of the metal-windings of the stator-coil, and/or the hollow-pipes form an integrated part of the slots of the laminate-plate.
 28. The arrangement according to claim 16, wherein the hollow pipes are made of metal or ceramic.
 29. The arrangement according to claim 16, wherein the electrical machine is a generator located inside a nacelle of a wind-turbine.
 30. The arrangement according to claim 16, wherein the electrical machine is totally encapsulated by a shell, so only air within the electrical machine is circulated for the air-cooling-purpose.
 31. A generator, comprising: a rotor; a stator; an air-gap arranged between the rotor and the stator; an air-cooling-arrangement that circulates air inside the electrical machine; a liquid-cooling-arrangement that circulates cooling-liquid inside the electrical machine; and a air-to-liquid heat-exchanger connects the air-cooling arrangement to the liquid-cooling-arrangement in order to transport heat out from the electrical machine by the cooling-liquid.
 32. The generator according to claim 31, wherein the stator comprises a plurality of laminate-plates, and the laminate-plates comprises a plurality of slots in which metal-windings of coils of the stator are arranged in the slots.
 33. The generator according to claim 31, wherein the stator is arranged as inner stator, while the rotor is arranged as outer rotor of the electrical machine.
 34. The generator according to claim 32, wherein the stator-coils exceed the slots of the laminate-plates to form winding-heads of the stator-coil.
 35. The generator according to claim 31, wherein the air-cooling arrangement comprises a fan. 